This invention relates to process technology for selective isomerization of vinylidene olefins to tri-substituted olefins, especially when the vinylidene olefins are in admixture with at least linear 1-olefins or remotely branched 1-olefins.
Mixtures of terminal olefins, commonly referred to as xcex1-olefins, are made commercially by ethylene chain growth of aluminum alkyls followed by displacement. Such products are mainly 1-olefins having the structure:
Rxe2x80x94CH2xe2x80x94CHxe2x95x90CH2
wherein R is an aliphatic hydrocarbon group. These are also referred to as xe2x80x9cvinyl olefinsxe2x80x9d. A substantial portion of the xcex1-olefins can be in the form of xe2x80x9cvinylidene olefinsxe2x80x9d which have the structure: 
wherein both R groups are aliphatic hydrocarbon groups.
One commercially important use of such xcex1-olefin mixtures is in the manufacture of aliphatic amines, especially alkyldimethyl amines, such as described in U.S. Pat. No. 4,024,189. In such processing, xcex1-olefin mixtures which contain vinyl olefins and vinylidene olefins are subjected to a selective isomerization step in which vinylidene olefins are converted to tri-substituted olefins. The entire mixture of olefins is then hydrobrominated to produce brominated alkanes. The brominated alkanes in turn are selectivity dehydrobrominated whereby secondary bromoalkanes are converted to olefins leaving the primary bromoalkanes substantially unaffected. Amination of the primary bromoalkanes results in production of the desired amines.
A number of isomerization catalysts capable of selectively isomerizing vinylidene olefins to tri-substituted olefins are known. See for example U.S. Pat. No. 3,686,250. While effective, such known catalysts often possess various shortcomings. For example, some of these catalysts are expensive, some may become inactivated or poisoned by impurities thus necessitating more frequent replenishment of the catalyst than would be desired, some of them tend to cause an undesirable amount of isomerization of linear 1-olefins to linear internal olefins, and some of them tend to cause dimerization of linear 1-olefins and of vinylidene olefins, which is also undesirable.
It would be of advantage if a new, efficient and commercially feasible way of selectively isomerizing vinylidene olefins to tri-substituted olefins could be found. It would be of particular advantage if this could be accomplished by use of a catalyst which is inexpensive, readily available, not susceptible to poisoning or inactivation under appropriate reaction conditions, that does not tend to excessively isomerize linear 1-olefins to linear internal olefins, and that does not tend to cause an excessive amount of dimer formation. This invention is believed to enable the achievement of most, if not all, of these advantages.
This invention is based in part on the discovery that vinylidene olefins can be rapidly and selectively isomerized to tri-substituted olefins by use of small quantities of anhydrous HBr. Surprisingly, by use of appropriate reaction conditions (e.g., absence of molecular oxygen whether in the form of air or otherwise, and free radical initiator), hydrobromination of the olefins can be avoided when conducting this selective isomerization.
Accordingly, pursuant to one of its embodiments, this invention provides a process of isomerizing at least one vinylidene olefin to at least one tri-substituted olefin, which process comprises contacting the mixture with anhydrous hydrogen bromide under anhydrous conditions and in the absence of molecular oxygen and free radical initiator, for a period of time sufficient to isomerize vinylidene olefin to tri-substituted olefin. In this process, little if any hydrobromination occurs. Usually, but not necessarily, the process of this embodiment is performed in the presence of at least one olefin that is not a vinylidene olefin or a tri-substituted olefin. In any case, the product recovered after the contacting is enriched in tri substituted olefin.
When the isomerization is performed in the presence of linear 1-olefins or remotely branched 1-olefins, the linear 1-olefins and the remotely branched 1-olefins are substantially unaffected. Thus in this case, the process is a selective isomerization process.
Accordingly, pursuant to another of its embodiments this invention provides a process for selective isomerization of at least one C10-20 vinylidene olefin to tri-substituted olefin in an anhydrous hydrocarbon mixture comprised of (i) at least one C10-20 vinylidene olefin, (ii) at least one C10-20 linear 1-olefin or (iii) at least one C10-20 remotely-branched 1-olefin, or (iv) a combination of (i), (ii) and (iii), and optionally (v) at least one C10-20 internal olefin or (vi) at least one saturated hydrocarbon, or (vii) both of (v) and (vi), while leaving the 1-olefins substantially unaffected during the isomerization, which process comprises contacting the mixture with anhydrous hydrogen bromide under anhydrous conditions and in the absence of molecular oxygen and free radical initiator for a period of time sufficient to selectively isomerize vinylidene olefin to tri-substituted olefin. As noted above little if any hydrobromination occurs in the process.
Another embodiment of this invention provides an improvement in a process for producing amines from a mixture of xcex1-olefins comprising vinylidene olefins and 1-olefins, wherein:
a) the mixture of olefins is subjected to selective isomerization to convert vinylidene olefins to tri-substituted olefins;
b) the olefin mixture resulting from the isomerization is hydrobrominated to form bromoalkanes comprising 1-bromoalkanes and secondary bromoalkanes and/or tertiary bromoalkanes;
c) bromoalkanes resulting from the hydrobromination are selectively dehydrobrominated whereby 1-bromoalkanes are substantially unaffected and secondary and/or tertiary bromoalkanes present are converted to olefins;
d) bromoalkanes from c) are aminated with an amine having at least one replaceable hydrogen atom whereby the 1-bromoalkanes are converted to amine hydrobromides, and
e) amine hydrobromides from d) are converted into amines.
Such a process has been commercially used. A full description of process technology of this type is present for example in U.S. Pat. No. 4,024,189. The improvement pursuant to this invention comprises effecting said selective isomerization by contacting said mixture of xcex1-olefins with anhydrous hydrogen bromide under anhydrous conditions and in the absence of molecular oxygen and free radical initiator for a period of time sufficient to selectively isomerize vinylidene olefin to tri-substituted olefin. Use of such selective isomerization leaves the 1-olefin content of the mixture substantially unaffected and in addition, little if any hydrobromination occurs. In addition, since one of the steps of this process involves hydrobromination, a source of anhydrous HBr is already available for use in the selective isomerization. Thus, no additional raw materials are required to carry out the isomerization.
Other embodiments and features of this invention will still be further apparent from the ensuing description and appended claims.
At the outset it is to be noted that the selective isomerization effected pursuant to this invention should not be confused with olefin hydrobromination processes in which anhydrous hydrogen bromide is added to an olefin mixture in order to produce brominated alkanes. A hydrobromination process is conducted in the presence of a substance functioning as a free radical initiator, and molecular oxygen such as in the form of air can function to initiate hydrobromination. Moreover, in hydrobromination processes a stoichiometric amount or an excess amount of hydrogen bromide relative to olefin is employed. In the isomerization process of this invention, air (and molecular oxygen in any mixture) is excluded from the reaction mixture, and no substance is introduced into the system to function as a free radical initiator. And, little if any hydrobromination occurs. Thus even though in a hydrobromination process, hydrogen bromide and olefin are contacted with each other, both the composition of the reaction mixture and the composition of the products of the process differ materially from the isomerization process of this invention.
To assist those who may be unfamiliar with the technology associated with xcex1-olefins, it is believed useful to explain some of the terms that are used by those of ordinary skill in this art. Accordingly, as used herein and as used by those of ordinary skill in this art:
1) Linear 1-olefins are compounds of the formula
Rxe2x80x94CH2xe2x80x94CHxe2x95x90CH2
where R is a straight chain alkyl group.
2) Remotely branched 1-olefins are compounds of the formula 
where each R is an alkyl group, and n is an integer which can be zero.
3) Linear internal olefins are compounds of the formulas 
where each R is an alkyl group.
4) Tri-substituted olefins are compounds of the formula 
where each R is an alkyl group. It will be noted that tri-substituted olefins do have an. internal double bond and thus are a special type of internal olefins.
The xcex1-olefin mixtures used in the practice of this invention will typically contain (a) at least one C10-20 vinylidene olefin and (b) at least one C10-20 linear 1-olefin or (c) at least one C10-20 remotely-branched 1-olefin, or (d) a combination of at least (a), (b), and (c), and optionally (e) at least one C10-20 internal olefin or (f) at least one saturated hydrocarbon, or (g) both of (e) and (f). Preferably, the olefins present in the initial mixture have in the range of about 12 to about 16 carbon atoms permolecule. A particularly preferred starting mixture of olefins is one in which the olefins are substantially entirely C14 olefins. The saturated hydrocarbon if present can be present as an impurity or it can be present as an inert diluent or solvent. Usually the use of a separate solvent is unnecessary unless the xcex1-olefin mixture to be used contains undissolved solid components.
The conditions used in carrying out the selective isomerization pursuant to this invention can be varied within reasonable limits. Typically the amount of anhydrous hydrogen bromide used will be in the range of about 0.05 mole to about 1.5 moles per mole of olefins present in the initial olefin mixture being used in the process. Desirably, this amount is in the range of about 0.05 mole to about 0.4 mole of hydrogen bromide or in the range of about 0.1 to about 0.4 mole of hydrogen bromide per mole of olefins present in the olefin mixture. Preferred proportions are in the range of about 0.05 mole to about 0.3 mole of hydrogen bromide per mole of olefins present in the initial olefin mixture.
Typically the isomerization is performed with the isomerization mixture or reactor contents at a temperature in the range of about xe2x88x9220xc2x0 C. to about 100xc2x0 C., and preferably at a temperature in the range of about 10xc2x0 C. to about 50xc2x0 C. A particularly preferred embodiment involves performing the isomerization with the isomerization mixture or reactor contents at a temperature in the range of about 20xc2x0 C. to about 30xc2x0 C.
The time period during which the isomerization is carried out is typically less than about 100 minutes and preferably is less than about 20 minutes. It is particularly preferred to carry out the isomerization in a period of up to 5 minutes, e.g., during a period in the range of about 1 to about 5 minutes.
In carrying out the isomerization, it is preferred to feed the olefins and the anhydrous HBr in the absence of molecular oxygen (air, etc.), and free radical initiator into a plug flow reactor. As is well known, reactors of this type are designed to enable all of the reaction components to flow as a stream through the reactor ideally at the same or essentially the same velocity with minimal back-mixing. For further details concerning plug flow reactors, one may refer for example to Octave Levenspiel, Chemical Reaction Engineering, 2nd Edition, John Wiley and Sons, Pub., Copyright 1972, pages 97 and 107-115.
If it is desired to remove the HBr from the product of the olefin isomerization, this can be done very efficiently simply by passing the reaction product into and through a water scrubber to dissolve the HBr from the product mixture. If desired, the purified isomerized olefins can then be dried before being stored or put to use. If on the other hand the product from the isomerization is to be used in the manufacture of amines by an improved process of this invention, removal of the HBr is unnecessary as the next step in the process is hydrobromination. Thus the HBr used in the isomerization can be left in the product mixture so as to form part of the HBr used in the hydrobromination. To this extent such HBr would serve a dual role in the process.